Fire-retardant tape utilizing an intumescent coating



Aug. 15,1967 w, JUDA 3,336,153

COATING' 3 3 FIG.

. FfRE-RETARDANT TAPE UTILIZING AN INTUMESCENT COATING Filed May. 22, 1963 WA LL 5 ADHESIVE 4 '--BACKING 2 INTUMESCENT WALTER JUDA, INVENTOR.

BY IEV M Mm ATTORNEYS United States Patent Office 3,336,153 FIRE-RETARDANT TAPE UTILIZING AN INTUMESCENT COATING Walter Juda, Lexington, Mass., assignor to Prototech Incltirporated, Cambridge, Mass., a corporation of Massac usetts Filed May 22, 1963, Ser. No. 282,495 5 Claims. (Cl. 117-685) The present invention relates to fire-retardant tapes and similar sheet material, being more particularly directed to fire-retardant tapes or the like that are applicable to a surface-to-be-protected.

In order to render combustible or other heat-sensitive structures fire retardant, the present practice often is to apply a fire-retardant coating to the structure. The coatings used for this purpose are usually liquid in form prior to application and may be applied by brush or by the use of a spray or roller. The coating thereafter dries and/or cures to form a durable surface. The most effec tive fire-retardant coating is an intumescent coating (described, for. example, in United States Letters Patents 2,106,938, 2,628,946, 2,650,206, 2,984,640 and other patents and publications) which may be applied in a substantially thin layer to a surface, but which, when subjected to, for example, flame temperatures, changes to a thick, carbonaceous, foam-like structure having good heat-insulating and fire-retardant characteristics. The application of the intumescent material to a surface by spraying or the like usually requires cleaning of the surface prior to the depositing of one or more coatings. This procedure is thus time-consuming and expensive. The use of such material has, therefore, not been widespread. Furthermore, it is practically impossible so to apply a uniform coating over the whole surface, so that uniform protection is difficult to obtain.

Non-intumescent non-inflammable materials, moreover, have also been used to impregnate band-ages and the like; but this kind of treatment merely protects the bandage fabric itself and is not adapted for the purposes of the present invention.

An object of the present invention, accordingly, is to provide a new and improved fire-retardant tape or the like that shall not be subject to the above-described limitations, but that, to the contrary, enables the application of auniformly thick surface of intumescent material to a combustible or other heat-sensitive structure.

Another object is to provide a fire-retardant tape that will maintain its bond to the combustible, though subjected to substantial temperature.

Still another object is to provide a fire-retardant tape which is relatively flexible.

A further object is to provide a fire-retardant tape or the like of more general utility, also.

Other and still further objects will be evident in the description to follow and will be particularly pointed out in connection with the appended claims.

Generally, and by way of summary, the objects of the invention are attained in a fire-retardant tape comprising, in combination, a backing material capable of charring but infusible and dimensionally stable below its charring temperature; an intumescent coating bonded upon one surface of the backing material, the coating having an incipient intumescing temperature below the said charring temperature; and an adhesive disposed upon the other surface of-the backing material, the adhesive being temperature-stable at least up to the incipient intumescing temperature range. Typical preferred fire-retardant coatings may begin to intumesce at about 200 F., for example, although coatings with higher intumescent temperatures may be used with higher temperature stable adhesives.

3,336,153 Patented Aug. 15,1967

The invention will now be described in connection with the accompanying drawing, FIG. 1 of which is a perspective, partially cut away view, illustrating a fire-retardant tape of the present invention applied to a surface;

FIG. 2 shows the tape of FIG. 1 subsequent to the application of high flame heat to the said tape; and

FIG. 3 is a sectional view of a modification.

Referring to FIG. 1, a fire-retardant tape 1 is shown comprising a backing material 2, which may, for example, be paper, cellulose fabric or a plastic film, preferably of 0.5 to 50 mils in thickness, serving as a supporting means. The backing material 2 is capable of charring but is infusible and dimensionally stable below its charring temperature in order to maintain its bond to a surface, such as the wall 5, in the presence of heat, as later discussed. An intumescent fire-retardant material is bonded or applied in a substantially thin layer or coating 3, preferably from 1 to 30 mils in thickness, to one major surface of the backing material 2. A temperature-stable adhesive 4 is applied upon the other major surface thereof to enable bonding of the tape 1 to a combustible-to-beprotected.

The tape herein described may be applied to the combustible itself, such as the wall 5, or it may be applied to a housing within which the combustible is disposed, as in the case of the walls of a safe within which papers or the like are stored. As will be described in detail hereinafter, upon the application of flame temperature to the intumescent coating 3, it changes to a thick carbonaceous foamed layer, shown at 6 in FIG. 2, having good insulating characteristics.

Paper has been found to be especially suitable for use as a backing material 2 both because of its stability up to its charring temperature and its relatively low cost. A useful paper for this purpose, as an illustration, is a wetstrength crepe paper, such as #311 Aqualized Duracel crepe paper, having a ream weight of 27 pounds (weight of 480 sheets-24" x 36"), marketed by Brown Paper Company. It is dip-saturated with a curable butadieneacrylonitrile copolymer latex (as Hycar OR-25 marketed by B. F. Goodrich Chemical Company). The paper is then coated on one of its major surfaces with about two ounces per square yard of a rubbery-based pressuresensitive adhesive, preferably one which is normally tacky. Before use the adhesive may be covered, for convenience, with a paper layer. A product particularly satisfactory for the purpose of the present invention is a normally tacky and pressure-sensitive adhesive coated creped paper having a caliper of approximately 9 mils, a machine direction tensile strength of about 19 pounds per inch of width, an elongation at break of 10%. Such a tape is available commercially from Minnesota Mining and Manufacturing Co. as SCOTCH Brand Pressure Sensitive Tape #209 (4MSK).

The characteristics of the intumescent material 3, as discussed in the said Letters Patent and in other publications, are such that upon the application of flame temperatures thereto, as in a fire, it changes to the thick carbonaceous foam-like layer 6, having good heat-insulating and fire-retardant characteristics; a few mils thickness of initial coating 3, for example, may result in a one-quarter to one-half inch thickness of expanded intumescent material upon the application of heat. To enable the backing material 2 to maintain its before-mentioned stable characteristics, the intumescent coating 3 must have an intumescing temperature below the said charring temperature. Once the intumescing temperature is reached, the heat energy applied is consumed in changing the character of the intumescent material so that the temperature remains below the said charring temperature. Subsequently, the thick carbonaceous layer 6 acts as an insulator for the backing material 2.

The intumescent coating 3 may be applied to the backing material 2 by, for example, spraying or by spreading the coating in liquid form upon a horizontally disposed substantially planar backing and controlling the thickness with an accurately positioned knife blade. The backing may be moved to one or more stations at each of which a thin coating is applied with an appropriate drying or curing step after each station. If Alibi 107A, later discussed, is used as the fire retardant, for example, the sprayed-on coating may be dried at about 160 F. for periods of one-half to one hour. In this manner, a desired uniform thickness of coating may be effected. Further, since the application of the coating is under condition susceptible of control, the thickness and composition of the coating 3, can be maintained within precise predetermined limits, preferably between one and 30 mils.

The intumescent material is applied as a liquid, but is often somewhat brittle once it sets or cures. When flexible coatings and flexible tapes are desired, it has been found that the intumescent material may be rendered pliable by the addition thereto of a small amount of compatible plasticizer. The addition of between one and per cent by weight of the liquid of a commercially available plasticizer has been found to render the intumescent material adequately pliable for purposes herein discussed. For example, when Citroflexf (that is, acetyltriethyl citrate ester plasticizer) or triethylene glycol or like compatible plasticizers is added to Alibi 107A, a commercially available intumescent fire-retardant paint of the type described, for example, in United States Letters Patent 2,984,640 (Examples 6 and/or 7), the material may be applied to a flexible backing 2 and the resultant product is sufficiently flexible to be rolled without cracking the intumescent layer. The plasticizer may be mixed with the intumescent material just prior to the application thereof to the backing material 2 or long prior to such application. The plasticizer, in the amounts above indicated, effects no significant change in the fire-retardant characteristics of the intumescent material.

The adhesive 4 must be temperature stable within the temperature range of interest, as has been discussed, and that is at least up to the incipient intumescing temperature and preferably through the intumescing temperature range. It is necessary that the adhesive be temperature stable up to the said intumescing temperature in order to maintain the bond between the tape and a surface-to-beprotected, as the wall 5. It is desirable that the adhesive 4 be temperature stable up to nearly the charring temperature of the backing 2, since continued exposure to the flame subjects the heat insulating foam to a gradual increase in temperature. Initially, the heat energy of the flame is used in causing the formation of the heat insulating thick foam. The tape thereafter affords continued protection until the backing 2 chars, provided that the adhesive 4 is temperature stable up to the said charring temperature.

The adhesive 4 is preferably one-that is pressure-sensitive, that is, one that is normally tacky and requires merely that a pressure be exerted to effect adherence thereof to a surface. Typical tapes with pressure-sensitive adhesives as well as examples of pressure-sensitive adhesives may be found in Encyclopedia of Chemical Technology, vol. 1, pp. 199-201, published by The Interscience Encyclopedia, Inc., in 1947. For example, rubber based pressure-sensitive adhesives may be used in connection with the invention. Reference is also made to standard textbooks on adhesives, for example, Adhesion and Adhesives, edited by N. A. De Bruyne and R. Houwink, Elsevier Press, Inc., Houston, Tex. (1951) which describe the compositions and methods of manufacture of suitable adhesives requiring wetting, which may be also used in the present invention, as well as of suitable pressuresensitive adhesives. The types of adhesives that may be used are many; however, the adhesive used must be chemically and dimensionally stable at least up to the incipient intumescing temperature of the backing material 2. The

adhesive means, furthermore, may be one which is applied to both sides 4 and 4 of a further layer or support 2, as shown in FIG. 3. In this case, the adhesive means may be applied separately to the wall 5 and the combination comprising the backing material 2 and intumescent coating 3 is affixed thereto, the said backing material being applied to the adhesive 4".

It may be desirable, in some applications, to improve the appearance of the intumescent coating, as by coloring, glass or other fibers, or other decorative layers.

Other applications to which the invention may be put include the covering or wrapping of objects that are to be subjected to high temperatures, such as, for example, the taping of electrical or other wires or conduits that may be subjected to high temperatures in combustion processes or the like.

An example of the efficacy of the present invention is afforded by tests on birch panels about 12 inches by 6 inches in dimension, coated by fire-retardant tape of the above-described character, as shown in FIG. 1. The method of testing was the standard Cabinet Method specified by the Department of Defense ASTM D1360-58. A weight loss of approximately 3 grams in this test was obtained, which is far better than the permissible 15 grams.

Other tests of a different character with the said tape applied to cardboard strips that, without the tape would burst into flame after about 5 seconds of exposure to a Bunsen burner flame, permitted exposure to the flame for from 4 to 6 minutes before the cardboard even commenced to char on the back surface.

Further modifications will occur to those skilled in the art and all such are considered to be within the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. A fire-retardant tape for application to a heat-sensitive surface-to-be-protected, consisting essentially of a backing material from substantially 0.5 to 50 mils in thickness, capable of charring but infusible and dimensionally stable below the charring temperature, a substantially uniform intumescent coating of from substantially 1 to 30 mils in thickness, bonded upon one surface of the backing material, the coating having an incipient intumescing temperature below the said charring temperature, and an adhesive disposed upon the other surface of the backing material, the adhesive being temperaturestable at least up to the said incipient intumescing temperature and adapted to aflix the tape to said surface-tobe-protected.

2. A fire-retardant tape as claimed in claim 1 and in which said backing material is cellulose material.

3. A fire-retardant tape as claimed in claim 1 and in which the backing material is paper.

4. A fire-retardant tape as claimed in claim 1 and in which the adhesive is a pressure-sensitive tacky adhesive.

5. A fire-retardant tape as claimed in claim 1 and in which said coating contains a small quantity of a plasticizer intimately mixed therewith to render the coating pliable, the plasticizer being selected from .triethylene glycol and acetyltriethyl citrate in an amount between substantially 1 to 10 percent of the wet weight of the coating.

References Cited UNITED STATES PATENTS 2,628,946 2/1953 Juda et a1 117-127 2,648,641 8/1953 Robison 117l36 2,650,206 8/1953 Stock 1l7137 2,725,981 12/1955 Abere et al. 1l768.5 2,912,394 1l/l959 Stilbert et a1 ll7-136 2,984,640 5/1961 Kaplan 117136 3,037,951 6/1962 Basto et al 1l7137 3,212,925 10/1965 Rosenthal et al l17-137 WILLIAM D. MARTIN, Primary Examiner.

W. D. HERRICK, Assistant Examiner. 

1. A FIRE-RETARDANT TAPE FOR APPLICATION TO A HEAT-SENSITIVE SURFACE-TO-BE-PROTECTED, CONSISTING ESSENTIALLY OF A BACKING MATERIAL FROM SUBSTANTIALLY 0.5 TO 50 MILS IN THICKNESS, CAPABLE OF CHARRING BUT INFUSIBLE AND DIMENSIONALLY STABLE BELOW THE CHARRING TEMPERATURE, A SUBSTANTIALLY UNIFORM INTUMESCENT COATING OF FROM SUBSTANTIALLY 1 TO 30 MILS IN THICKNESS, BONDED UPON ONE SURFACE OF THE BACKING MATERIAL, THE COATING HAVING AN INCIPIENT INTUMESCING TEMPERATURE BELOW THE SAID CHARRING TEMPERATURE, AND AN ADHESIVE DISPOSED UPON THE OTHER SURFACE OF THE BACKING MATERIAL, THE ADHESIVE BEING TEMPERATURESTABLE AT LEAST UP TO THE SAID INCIPIENT INTUMESCING TEMPERATURE AND ADAPTED TO AFFIX THE TAPE TO SAID SURFACE-TOBE-PROTECTED. 